A rhodium-catalyzed alkylation reaction of indoles with N-Boc-imines has been developed via C-H activation to afford a series of substituted 2-indolyl-methanamine derivatives with good functional group tolerance and regioselectivity. A wide range of indole-based alkylation products could be obtained in up to 95% yield.
Keywords:
rhodium(III)-catalysis; C-H activation; indole
| entry | Catalyst | Solvent | Additive | Temperature / ºC | time / h | Yieldb b yield of isolated product; / % |
|---|---|---|---|---|---|---|
| 1 | [Cp*RhCl2]2 | DCE | - | 75 | 6 | 0 |
| 2 | [Cp*RhCl2]2 | DCE | AgCO2CF3 | 75 | 6 | 30 |
| 3 | [Cp*RhCl2]2 | DCE | AgSO3CF3 | 75 | 6 | 37 |
| 4 | [Cp*RhCl2]2 | DCE | AgSbF6 | 75 | 6 | 85 |
| 5c c the reaction was carried out under air; | [Cp*RhCl2]2 | DCE | AgSbF6 | 75 | 6 | 34 |
| 6 | [Cp*RhCl2]2 | PhMe | AgSbF6 | 75 | 24 | 61 |
| 7 | [Cp*RhCl2]2 | t-BuOH | AgSbF6 | 75 | 24 | 23 |
| 8 | [Cp*RhCl2]2 | DCM | AgSbF6 | 75 | 6 | 71 |
| 9d d the amount of catalyst was decreased to 2.5 mol%; | [Cp*RhCl2]2 | DCE | AgSbF6 | 75 | 6 | 47 |
| 10e e the amount of additive was decreased to 10 mol%; DCE: 1,2-dichloroethane; PhMe: toluene; t-BuOH: tert-butyl alcohol; DCM: dichloromethane. | [Cp*RhCl2]2 | DCE | AgSbF6 | 75 | 6 | 62 |
| 11 | [Cp*RhCl2]2 | DCE | AgSbF6 | 25 | 6 | 72 |
| 12 | [Cp*RhCl2]2 | DCE | AgSbF6 | 50 | 6 | 68 |
